Improve wave length guessing

Instead of assuming that wav files have 44 byte headers (they usually
don't - freeswitch adds some metadata tags), add a super-simple wave
file parser that just finds the offset where the audio data actually
starts.

record-and-playback/core/lib/recordandplayback/edl/audio.rb

@@ -186,7 +186,8 @@ module BigBlueButton
             # wav files generated by freeswitch can have incorrect length
             # field if longer than 4GB, so recalculate based on filesize (ouch!)
             BigBlueButton.logger.debug("Recalculated duration from wav file length")
-            audio_size = info[:format][:size].to_r - 44 # wav header is 44 bytes
+            audio_offset = self.get_wave_data_offset(filename)
+            audio_size = info[:format][:size].to_r - audio_offset
             info[:duration] = (audio_size * 8 / info[:audio][:bit_rate].to_i * 1000).to_i
           else
             info[:duration] = (info[:format][:duration].to_r * 1000).to_i
@@ -202,6 +203,32 @@ module BigBlueButton
         ms = timestamp % 1000
         "%d.%03d" % [s, ms]
       end
+
+      # Helper function for determining correct length of freeswitch's long wave files
+      def self.get_wave_data_offset(filename)
+        File.open(filename, 'rb') do |file|
+          riff = file.read(4)
+          wavesize = file.read(4).unpack('V')[0].to_i
+          wave = file.read(4)
+          if riff != 'RIFF' or wavesize.nil? or wave != 'WAVE'
+            return 0
+          end
+          while true
+            # Read chunks until we find one named 'data'
+            chunkname = file.read(4)
+            chunksize = file.read(4).unpack('V')[0].to_i
+            if chunkname.nil? or chunksize.nil?
+              return 0
+            end
+            if chunkname == 'data'
+              # This is a data chunk; we've found the start of the real audio data
+              return file.tell
+            end
+            file.seek(chunksize, IO::SEEK_CUR)
+          end
+          return 0
+        end
+      end
     end
   end
 end